Disc transfer devices to petri dishes

ABSTRACT

A disc transfer device for loading a Petri dish. The transfer device includes a plurality of storage tubes with stacks of discs of blotting paper which are, for example, impregnated with an antibiotic to be evaluated. A transfer plate displaces the discs at the bottom of their respective stacks to ejection locations in alignment with ejection passageways which have diameters slightly less than that of the discs thereby preventing the free fall of the discs onto the gelose medium. A control shaft is rotatable for displacing the transfer plate from its disc receiving position to its ejection position and slidably movable perpendicular to the receiving surface for descending plungers which drive the discs to the receiving surface. All the discs are brought into contact with the germ seeded gelose medium in the Petri dish with exactly the same contact pressure, reproductible from cycle to cycle, this pressure being determined by the mass of the plungers. The Petri box is provided with various indicia including intersecting perpendicular lines on its outer bottom wall for aiding the determination of the germ inhibiting zone measured by the discs in position at the intersections.

United States Patent [191 [111 3,863,426 Courvalin Feb. 4, 1975 DISCTRANSFER DEVICES TO PETRI Primary Examiner-Robert L. Spruill DISHESAttorney, Agent, or Firm-Diller, Brown, Ramik & [75] Inventor: PatriceMarie Denis Paul Courvalin, Wight Paris, France [73] Assignee: AgenceNationale de Valorisation de [57] ABSTRACT la Recherche, Neuilhhsugseine A disc transfer device for loading a Petri dish. The (Hauts deseine) prance transfer device includes a plurality of storage tubes withstacks of discs of blotting paper which are, for ex- [22] May 1973ample, impregnated with an antibiotic to be evaluated. [21] APPL 3 4 0 4A transfer plate displaces the discs at the bottom of their respectivestacks to ejection locations in alignment with ejection passagewayswhich have diameters slightly less than that of the discs therebypreventing [30] Foreign Application Priority Data the free fall of thediscs onto the gelose medium. A a control shaft is rotatable fordisplacing the transfer May 26, I972 France 72.018905 plate from itsdisc receiving position to its e ection po- 'tion and slidabl movable erendicular to the re- 52 us. Cl 53/237, 53/247 53/390 y p ceivmg surfacefor descending plungers which drive Int Cl B65) the discs to thereceiving surface. All the discs are 58 brought into contact with thegerm seeded gelose mere d o earch 53/166, 235, 237, 247,

53/254, 221/93, 132, 224 225, drum in the Petri d sh with exactly thesame contact 232 233 270 pressure, reproductible from cycle to cycle,this pressure being determined by the mass of the plungers.

The Petri box is provided with various indicia including intersectingperpendicular lines on its outer bot- [56] References Cted tom wall foraiding the determination of the germ in- UNITED STATES PATENTS hibitingzone measured by the discs in position at the 2,339,115 1/1944 Scherer53/166 x intersections- 3,03l,8l9 51962 M l t l. 3,394,846 7i196s 15Clams 11 Drawmg F'gures PATENTED FEB 4 75 SHEET 10F 3 mwwwwwmmmmvmi t mN PATENTEU FEB 75 SHEET 2 BF 3 1 DISC TRANSFER DEVICES TO PETRI DISHESThe present invention relates to an improved device for the transfer offlat objects such as discs to a receiving surface. For the sake ofclarity and simplicity the flat articles which are to be transferred tothe receiving surface, as will be described below, are uniformlydesignated as discs; it is obvious, however, that this term is notintended as a limitation as to their configuration or shape.

This type of transfer device is employed for the simultaneouspositioning of discs impregnated with different substances, antibioticsfor example, for qualitative evaluation according to a particularcharacteristic; in the case of antibiotics, this is their activity withrespect to a certain germ (micro-organism The qualitative evaluation isproduced in the form of an antibiogram which is a visual representationof antibiotic activity.

In order to construct such an antibiogram, the surface of a thin layerof a sterile gelose medium is seeded with the germ being studied; aftersuitable drying, the discs formed of blotting paper about 6 mm indiameter and about 0.8 mm in thickness, and previously impregnated withdifferent antibiotics being evaluated, are regularly distributed overthe surface of the seeded gelose medium. The combination is thenmaintained in an incubator for 18 hours at approximately 37C in order toenable the multiplication of the germ and the diffusion of theantibiotic through the medium. The reading of the antibiogram consistsof measuring the diameter of the germ growth inhibiting zone centered onthe disc. The discs, commonly less than 20 in number, are depositedindividually by means of tweezers or simultaneously by means of anautomatic transfer device.

The automatic transfer devices commonly used generally comprise severalstorage tubes each containing a stack of discs previously impregnatedwith a particular antibiotic. The maneuvering of ejection means enablesthe simultaneous discharge of a disc from each one of the storage tubesdropping them to the surface of the medium through a guidechannel.-These transfer devices are easy to operate but neverthelesshave the disadvantage of not being able to assure a satisfactory contactof the discs on the medium which may cause the displacement of the discin the course of subsequent handling, or an irregular or partialdistribution of the antibiotic. In order to remedy the situation, theoperator is obligated to carefully press each disc down so as to obtainintimate contact between the disc and the medium. It frequently occursthat the disc turns during its fall which complicates subsequentidentification in the case of discs printed on only one face. It evenhappens that the disc rolls along the surface of the medium dischargingpart of its contents which invalidates the results of the antibiogram.

An aim of the invention consists in overcoming the drawbacks as well asthe errors and loss of time in prior automatic transfer devices.

One aspect of the invention consists in a transfer device for depositingdiscs on the receiving surface of a Petri dish. comprising a casing withits bottom facing the receiving surface, a plurality of tubes mounted inthe casing for storing stacks of discs, transfer means for transferringthe disc at the bottom of each stack to an ejection position inalignment with a corresponding plurality of ejection passageways, aplurality of plungers arranged in alignment with said ejectionpassageways for sliding movement perpendicular to the bottom of thecasing towards the receiving surface for driving the discs from theirejection position through said passageways onto the receiving surface.

Preferably, the plungers have a predetermined weight defining thepressure of application of the discs on the receiving surface.

Preferably, the cross section of the ejection passageways is slightlysmaller than the cross section of the discs thereby preventing the freefall of the discs to the receiving surface without the force exerted bythe plungers.

Preferably, the transfer device has a control shaft rotatably mountedfor transferring the disc to the ejection position and slidably mountedfor driving the discs to the receiving surface.

Advantageously, the bottom of the casing is adapted to cooperate withthe side walls of the Petri dish, the said receiving surface being thebottom wall of the Petri dish.

The Petri dish is preferably of square shape and the bottom of the Petridish has a network of spaced perpendicular lines parallel to the sidesof the dish, the points of intersection of the lines defining points ofapplication of the discs.

A principal advantage of the present transfer device is that drives thediscs to the receiving surface with a precise, reproducible forceassuring the desired contact between the disc and the receiving surface.

In the preferred field of application in combination with a Petri dish,the present transfer device drives the discs through the passagewaysonto the gelose medium depositing the discs thereon with a precisepredetermined, reproducible force assuring the desired contact betweenthe disc and the gelose medium.

Further featuresand advantages of the transfer device and Petri dishaccording to the present invention will be brought out in thedescription which follows with reference to the accompanying drawings,in which:

FIG. 1 is a plan view of the base of the transfer device showing themounting of the system of storage tubes and associated ejectionpassageways;

FIG. 2 is a sectional view taken along the line ll-ll in FIG. 1;

FIG. 3 is a sectional view taken along the line Ill-Ill in FIG. 1;

FIG. 4 is a sectional view similar to FIG. 2 with the control knob inits upper position after being turned through FIG. 5 is a sectional viewsimilar to FIG. 4 in which the control knob is brought into position bydownward displacement after rotation;

FIGS. 6 and 7 are details in perspective on an enlarged scale, partly insection of a storage tube and an associated ejecting means which isshown in two different positions; and

FIGS. 8-11 show a preferred embodiment illustrating the Petri dishadapted to be associated with the transfer device shown in FIGS. 1-7 andits cover.

Reference will now be made to FIGS. 1-3 in which a transfer devicedesignated generally by the reference numeral 1 is shown in position ona Petri dish 2, the bottom of the Petri dish being covered with a layerof gelose medium providing a receiving surface 3. The transfer device Iessentially comprises a casing 4 receiving the disc storage tubes 5, aplaten 6 carrying push members or plungers 7 as well as a control shaft8 with a knob 9 at its outer end. The casing 4 comprises a body 10 witha base 11 and a cover 12. The outwardly projecting portions 13 on thebase 11 rest against the sides of the Petri dish so that the lower face14 of the base is at a predetermined distance from the gelose layer onthe plate or receiving surface 3.

A series of cylindrical recesses 16 receive the lower ends of thestorage tubes 5 and a series of bores which form ejection passagewaysfor depositing the discs on the receiving surface 3 are provided in thebase 11.

In the illustrated embodiment the platen 6 comprises upper and lowerplates 17 and 18 between which the flange 19 of the spindle 8 is held.The platen 6 is thereby secured to the spindle 8 for verticaldisplacement therewith. Heads of the plungers 7 are in rubbing contactand slidable along cylinders 21 formed in the platen 6, the cylinders 21being slightly longer in axial dimensions than the heads 20.

The bottom of each of the storage tubes 5 keyed in an associated recess16 is formed as a dimetral stirruplike member having transverse slots 23(FIGS. 6 and 7) defining openings adapted to the dimensions of the discsbeing handled.

The upper end of each storage tube 5 is provided with resilient means(not illustrated) acting against the stack of discs for assuring theregular descent thereof according to the transfer cycle. The storagetubes 5 pass freely through the bores in the platen 6 and the cover 12and are held in position by a horizontally displaceable locking plate 24for the storage tubes responsive to a vertical force acting against thetop portion of symmetrically oriented radial projections 25 arranged ata suitable position along the storage tubes 5. A pair of push buttons 26and 27 each projecting from one side of the casing 4 permit the lockingand unlocking of the storage tubes 5.

The transfer plate 28 is linearly slidably mounted on the base 11 of thecasing and has a series of apertures 29 (FIGS. 6 and 7) each defining atransfer tongue 30 flanked by slots 31 providing passage to the bottomof the storage tube. The leading edge 32 of the tongue 30 shaped toconform to the shape of the disc, is illustrated in its rearawardposition in FIG. 4, i.e., in horizontal and vertical alignment with thedisc being transferred; and in its forward position in FIG. 7, the disc33 having been displaced, as will be explained below. is in verticalalignment with the associated ejection passageway 15.

The displacement of the transfer plate 28 is controlled by the controlspindle 8 in the following manner: a pivot 34 coaxial with the controlspindle 8 and received in the base (FIGS. 1 and 2) has at its upper endpulley 35 with a lateral tab 36. A blind axial socket 37 of square crosssection in the illustrated embodiment of FIG. I is arranged in thepulley 34. The lower end of a rod 38 also of a square cross section isreceived in the socket 37. Moreover, one end of a traction cord issecured to the slide 39 coupled to the plate 28 at one side of the plateperpendicular to the direction of displacement. The other end of thecord is partly wound around the pulley 35 and connected to the tab 36.Clockwise rotation of the rod 38 therefore effects the displacement ofthe slide 39 and the transfer plate 28 in the direction of the arrow(FIG. 2).

The abutting of the slide 39 with the end of its housing preciselylimits the path of movement of the transfer plate 28 which at the end ofthe cycle is returned to the starting position by return springs 41schematically represented in FIG. 1.

Once the linear transfer movement of the transfer plate 28 has beeninititated by the rotation of the pulley 35, retractable abutment means42 shown in FIGS. 2, 4 and 5, comprising a leaf spring 43 inserted atone end in a swinging lever 44 while the other end of the leaf springcooperates with a stop 45 on a slide 46 connected for movement with theplate 28, prevents the rearward movement of the plate 28 by the springs41. At the end of the transfer cycle, the return of the slide 46 effectsthe resetting of the leaf spring 43.

The control spindle 8 has a tubular body 47 slidably and pivotallymounted in a sleeve 48, the lower end of the sleeve being secured to thecover 12. The body 47 ends with the flanged socket portion 49 which asdescribed above is held in a cylindrical bore 50 in the platen 6. Themounting couples the platen 6 and the body 47 for up-and-downreciprocating movement but enables the free rotation of the socket 49 inthe bore 50 and therefore the body 47. This socket 49 has a squareinterior cross section adapted to receive in rubbing contact for slidingmovement the free end of the rod 38 coupled at its lower end to thepulley.

A guide plate 51 overlying the transfer plate 28 is provided for guidingthe lower end of the plungers 7. The guide plate 51 has a plurality ofbores 52 arranged along the axes of the ejection passageways 15 as wellas for freely receiving the bases of the disc storage tubes 5.

The platen 6 is held in its upper position by springs 53 (FIGS. 1 and 3)guided in the tubular members 54 resting on the guide plate 51 andinserted at their upper ends in the cover 12. T-shaped keys 55 are heldcaptive in the plate 6, the cross bars thereof extending into theapertures in the tubular members 54, said T-shaped keys providing abearing surface for the upper ends of the springs 53.

As it will be described hereinafter, the operation of the transferdevice comprises sequentially rotational then sliding lineardisplacement of the control spindle 8. For this purpose, the controlknob 8 is provided with a vertically depending finger or key 56 (FIG.4), the sleeve 47 having an opening 57 (FIG. 2) in which the finger orkey 56 can be received.

Interlocking means, not illustrated in detail in the drawings, controlsthe control spindle 8 depending on the position of the locking plate 24so that all rotational or sliding movement of the control spindle 8 isprevented when the locking plate 24 is not in its locked position.

The operation of the device as described above will now be described:

The storage tubes 5, once filled, are secured in position by the lockingplate 24; the finger or key 56 rests on the sleeve 48 at a predeterminedangular distance from the opening 57. The platen 6 is maintained in itsupper position by the springs 54 whereas the transfer plate 28 is heldin its rearward position by the springs 41. The head of each plungerrests on the bottom of its associated cylinder 21, the bottom of thepush members or plungers being in engagement with the associated bore inthe guide plate 51.

In the first phase of operation, the operator turns the control knob 9in the clockwise direction (arrow G in FIG. 1); the cord 40 pulls theslide 39 in the direction of the arrow F and each of the tongues of thetransfer plate 28 engage a disc at the bottom of a stack in acorresponding storage tube 5 to transfer the said disc to'an associatedejection passageway 16 (FIGS. 6 and 7) During the initial phase ofoperation, the retractable abutment means 42 protrudes to prevent thereturn of the transfer plate 28 until it has completed the movement ofthe discs to their ejection position and the discs arrive on thereceiving surface.

When the discs come into forward abutment against the slide 39 (FIG. 4),they are in vertical alignment with the ejection passageways 16, thefinger or key 56 on the control knob 8 being in alignment with theopening 57.

At a second phase of the operation, the operator exerts a forcedownwardly against the control knob 8 which brings about the descent ofthe platen 6 and the plungers 7. After passing through the guide plate51, the plungers come into contact with the transferred discs and drivethem down through the ejection passageways 16. The bores of thesepassageways are machined to a dimension slightly less than the discdiameter, for example 0.05 mm, so that only the positiive action of theplungers 7 is able to bring about the descent of the discs to thereceiving surface. When the platen 6 arrives at its lowermost position(FIG. 5), the ejected discs emerge from the passageways 16 with the endsof the plunger 7. As it was noted above, the cylinders 21 with which theheads are in slight frictional sliding contact have an axial dimensionslightly greater than that of the heads. From this fact it follows thatthe heads 20 which were in contact with the upper ends of the cylinders21 continue there descending path of movement by gravity until they cometo abut against the lower end of the cylinders. Consequently, theplungers 7 descend with the ejected discs and their free fall iscalculated so that the discs are applied against the receiving surface 3supporting the gelose medium by a force determined by the mass of theplunger which may therefore be precisely reproduced in another transferdevice.

Once the downwardly directed force exerted by the operator is released,the springs 53 return the platen and the knob 6 upwardly; as soon as thekey or finger 56 is out ofengagement with the opening 57 the springs 41act to return the transfer plate 28 to its rearward position while thecontrol knob 8 undergoes a counterclockwise rotational movementreturning it to the position shown in FIG. 2. The device 42 is resetduring the return path of movement of the transfer plate; the transferdevice is then ready for another transfer cycle.

Reference will now be made to FIGS. 8-11 showing an alternativeembodiment of the Petri dish (FIGS. 8 and 9) whose receiving surface isadapted to receive the discs deposited thereon by the present transferdevice. The cover therefor is shown in FIGS. and 11.

The dish generally designated by the reference numeral 60 has a flatbottom wall 61 and upstanding side walls 62 connected by fillets 63.Supporting feet 64 are arranged at the corners of the dish 60.

A network of perpendicular straight lines equidistant from one anotherand parallel to the sides of the dish are provided on the exterior faceof the bottom wall 61. The intersections of the perpendicular straightlines define points of application-for the centers of the discs. Thestraight lines may be shaped as ribs formed during the molding of thedish or etched grooves.

Graduated scales are provided at 66 and 67 centered at points ofintersection of the straight lines which may be millimetric or othersuitable scales, such as concentrations expressed in micrograms permilliliter. These inidicia or scales may be etched into the bottom wall61 or simply secured thereto by any suitable means, for example printedsheets readable through the transparent gelose medium and bottom wall.

The bottom wall could of course be provided with other indicia as afunction of the measurements to be effectuated.

The cover 68 (FIGS. 9 and 10) is adapted to be received on the dish 60and comprises a top wall 69 and a skirt which is fitted onto the sidewalls of the dish. Bosses 71 formed on the interior face of the top wall69 prevent the top wall from resting directly on the edge of the sidewalls. In this way the interior of the dish 60 with its cover 68 isaerated thereby avoiding the formation of condensation along theinterior face of the top wall of the cover which might interfere withreadings.

The cover 68 has a rim 72 adapted to receive the support feet of thedish 60 for stacking the dishes with their covers on top of one another.

The problems solved relative to the particular application concerned byan aspect of the invention include a. the determination of the minimuminhibiting concentrations of the germs relative to various antimicrobicagents (by the technique of diffusion in a jellied medium with the aidof correlating curves); and

b. the clinical categorization of the results.

The advantages of the transfer device in combination with the Petri dishas described above include:

I. automatic operation of the device whereby it is no longer necessaryto actually push each disc into the gelose medium;

2. the discs being put in contact with the gelose medium with the samereproducible pressure, the pressure exerted by each plunger being thesame and constant from cycle to cycle (the intimate contact of thediscswith the surface of the gelose medium assures excellent diffusionof the antibiotic therein);

3. the increase of the effective surface of the gelose medium owing tothe particular arrangement of the discs;

4. reduction in the number of errors; and

5. the qualitative and quantitative reading of the results being moreprecise, rapid and easy since the 16 discs positioned at theintersection of the network of perpendicular lines associated withgraduations marked on the outer face of the bottom of the box enable animmediate and precise reading of the diameter of inhibitor zone alongeach of two perpendicular axes.

It is preferable to deliver the dishes with the gelose medium therein(the thickness of the medium being about 4 mm). the variations of thediameter of the inhibitor zones due to the differences in the thicknessof the gelose medium can be thereby avoided.

It is also possible to eliminate overlapping of the inhibitor zones (theoverlapping creating qualitative reading errors) on the condition thatthe diameter of the zones does not exceed 30 mm which is generally notthe case.

The present invention is of course not limited to the illustrated anddescribed embodiment but, on the contrary, includes all alternatives andmodifications within the scope of the appending claims.

I claim: 1. A transfer device for depositing discs on a receivmovementperpendicular to the bottom of the casing towards the receiving surfacefor driving the discs from their ejection position through saidpassageways onto the receiving surface and single control means forsequentially actuating said transfer means and said plunger.

2. A transfer device according to claim 1, together with a platencarrying said plungers for simultaneous movement, and means individuallymounting each plunger on said platen for freedom-of movement relative tosaid platen in a direction away from the bottom of the casing whereinthe weight of each plunger defines the pressure with which eachdisc isapplied against the receiving surface.

3. A transfer device according to claim 1, wherein the cross section ofthe ejection passageways is smaller than the cross section of the discsfor which said tubes are intended to hold so as to prevent the free fallof the intended discs from their ejection position to the receivingsurface. I

4. A transfer device according to claim 3, wherein the largestlateraldimension of the intended discs exceeds the largest lateral dimension ofthe ejection passageways by 0.05 mm.

5. A transfer device according to claim 1, wherein the bottom of thecasing is adapted to cooperate with the side wall of a Petri dish toaccurately position said ejection passageways relative to the Petridish, the bottom wall of the Petri dish constituting the said receivingsurface.

6. A transfer device according to claim 5, further comprising anetworkof perpendicular lines parallel to the walls of the dish andequidistant from'one another, the intersections of said perpendicularlines defining the centers of both said ejection passageways and thepoints of application of the discs on the receiving surface.

7. A transfer device according to claim 1, wherein said single controlmeans includes a platen supporting all of said plungers for simultaneousmovement and a control shaft, means mounting said control shaft forrotational movement relative to said platen and for conjoint axialmovement with said platen.

8. A transfer device according to claim 7, wherein therotationalmovement of the control shafteffectsthe displacementof thevtransfer means between its disc receiving positi'onand the ejectionpositiontand wherein the conjoint sliding movement of the control shafteffects in the downward direction the driving of the discs into contactwith the receiving surface.

,9. A transfer device according to claim 8, wherein means are providedto prevent the conjoint sliding movement of the platen with the controlshaft until the control shaft has been rotated to bring the discs totheir ejection position.

10. A transfer device according to claim 8, wherein the transfer meanscomprises a transfer plate, and further comprising retractable abutmentmeans-associated with the transfer plate for preventing its return toits disc receiving position until the discs brought to their ejectionposition are driven to the receiving surface.

11. A transfer device fordepositing discs on a receiving surface,comprising a casing having a bottom particularly adapted to face thereceiving surface, a plurality of tubes mounted inthe casing for storingstacks of discs, an ejection passageway in'said casing laterallyadjacent each stack, transfer means for transferring the disc at thebottom of each stack laterally to an ejection position in alignment witha corresponding one of said ejectionpassageways, a plurality of plungersarranged in alignment with said ejection passageways for slidingmovement perpendicular to the bottom of the casing towards thereceivingsurface for driving the discs from their ejection. position throughsaidpassageways onto the receiving surface, each plunger including a rod forsliding movement in its associated ejectionpassageway and a head, aplaten including a plurality of cylinders defined therein, 'and'eachplunger headbeing mounted for sliding'movement in an associated cylinderwhich determines the path of movement of the plunger.

12. A transfer device according to claim 11', further comprising acontrol shaft, said control shaft being mounted for rotational movementrelative to the platen and conjoint axial movement with said platen.

13. A transfer device according to claim 12, wherein the rotationalmovement of the control shaft effects the displacement of the transfermeans between its disc receiving position and the ejection position; andwherein the conjoint sliding movement of the control shaft effects inthe downward direction the driving of the discs into contact with thereceiving surface.

14. A transfer device according to claim 13, wherein means are providedto prevent. the conjoint sliding movement of the platen with the controlshaft until the control shaft has been rotated to bring the discs totheir ejection position. i

15. A transfer device according to claim 13, wherein the transfer meanscomprises a transfer plate,-and further comprisingretractable abutmentmeans associated with the transfer plate for preventing its return toits disc receiving position until the discs brought to their ejectionposition are driven to the receiving surface.

. l i 1' ll! ll

1. A transfer device for depositing discs on a receiving surface,comprising a casing having a bottom particularly adapted to face thereceiving surface, a plurality of tubes mounted in the casing forstoring stacks of discs, an ejection passageway in said casing laterallyadjacent each stack, transfer means for transferring the disc at thebottom of each stack laterally to an ejection position in alignment witha corresponding one of said ejection passageways, a plurality ofplungers arranged in alignment with said ejection passageways forsliding movement perpendicular to the bottom of the casing towards thereceiving surface for driving the discs from their ejection positionthrough said passageways onto the receiving surface and single controlmeans for sequentially actuating said transfer means and said plunger.2. A transfer device according to claim 1, together with a platencarrying said plungers for simultaneous movement, and means individuallymounting each plunger on said platen for freedom of movement relative tosaid platen in a direction away from the bottom of the casing whereinthe weight of each plunger defines the pressure with which each disc isapplied against the receiving surface.
 3. A transfer device according toclaim 1, wherein the cross section of the ejection passageways issmaller than the cross section of the discs for which said tubes areintended to hold so as to prevent the free fall of the intended discsfrom their ejection position to the receiving Surface.
 4. A transferdevice according to claim 3, wherein the largest lateral dimension ofthe intended discs exceeds the largest lateral dimension of the ejectionpassageways by 0.05 mm.
 5. A transfer device according to claim 1,wherein the bottom of the casing is adapted to cooperate with the sidewall of a Petri dish to accurately position said ejection passagewaysrelative to the Petri dish, the bottom wall of the Petri dishconstituting the said receiving surface.
 6. A transfer device accordingto claim 5, further comprising a network of perpendicular lines parallelto the walls of the dish and equidistant from one another, theintersections of said perpendicular lines defining the centers of bothsaid ejection passageways and the points of application of the discs onthe receiving surface.
 7. A transfer device according to claim 1,wherein said single control means includes a platen supporting all ofsaid plungers for simultaneous movement and a control shaft, meansmounting said control shaft for rotational movement relative to saidplaten and for conjoint axial movement with said platen.
 8. A transferdevice according to claim 7, wherein the rotational movement of thecontrol shaft effects the displacement of the transfer means between itsdisc receiving position and the ejection position; and wherein theconjoint sliding movement of the control shaft effects in the downwarddirection the driving of the discs into contact with the receivingsurface.
 9. A transfer device according to claim 8, wherein means areprovided to prevent the conjoint sliding movement of the platen with thecontrol shaft until the control shaft has been rotated to bring thediscs to their ejection position.
 10. A transfer device according toclaim 8, wherein the transfer means comprises a transfer plate, andfurther comprising retractable abutment means associated with thetransfer plate for preventing its return to its disc receiving positionuntil the discs brought to their ejection position are driven to thereceiving surface.
 11. A transfer device for depositing discs on areceiving surface, comprising a casing having a bottom particularlyadapted to face the receiving surface, a plurality of tubes mounted inthe casing for storing stacks of discs, an ejection passageway in saidcasing laterally adjacent each stack, transfer means for transferringthe disc at the bottom of each stack laterally to an ejection positionin alignment with a corresponding one of said ejection passageways, aplurality of plungers arranged in alignment with said ejectionpassageways for sliding movement perpendicular to the bottom of thecasing towards the receiving surface for driving the discs from theirejection position through said passageways onto the receiving surface,each plunger including a rod for sliding movement in its associatedejection passageway and a head, a platen including a plurality ofcylinders defined therein, and each plunger head being mounted forsliding movement in an associated cylinder which determines the path ofmovement of the plunger.
 12. A transfer device according to claim 11,further comprising a control shaft, said control shaft being mounted forrotational movement relative to the platen and conjoint axial movementwith said platen.
 13. A transfer device according to claim 12, whereinthe rotational movement of the control shaft effects the displacement ofthe transfer means between its disc receiving position and the ejectionposition; and wherein the conjoint sliding movement of the control shafteffects in the downward direction the driving of the discs into contactwith the receiving surface.
 14. A transfer device according to claim 13,wherein means are provided to prevent the conjoint sliding movement ofthe platen with the control shaft until the control shaft has beenrotated to bring the discs to their ejection position.
 15. A transferdevice according to claim 13, wherein the transfer means comprises atransFer plate, and further comprising retractable abutment meansassociated with the transfer plate for preventing its return to its discreceiving position until the discs brought to their ejection positionare driven to the receiving surface.